Method for rolling a metal strip

ABSTRACT

The invention relates to a method for rolling a metal strip ( 6 ) in a reverse rolling mill ( 1 ) with a coiler located upstream and a coiler located downstream ( 4,5 ). The metal strip is wound off the upstream coiler ( 4 ) with a strip thickness (d) and at a strip temperature (T) above a set temperature (T*). It is then passed through the reverse rolling mill ( 1 ) with a first draught of at most 5% and at a speed (v) before being wound up by the downstream coiler ( 5 ). The speed (v) at which the strip is passed through the rolling mill is selected with the aim of ensuring that the strip has reached the set temperature (T*) by the time it is wound up. The strip is then wound off the downstream coiler ( 5 ), passed through the reverse rolling mill ( 1 ) with a second draught of at least 10% and wound up by the upstream coiler ( 4 ).

The present invention relates to a method for rolling a metal strip,especially a steel strip, in a reverse rolling mill comprising a coilerupstream and a coiler downstream thereof, wherein the strip is removedfrom one of the coilers, passes through the reverse rolling mill with areduction per pass of at least 10%, and is then wound onto the othercoiler.

Such rolling mills and the corresponding methods for rolling are knownin general. In such rolling mills, the strip is rolled by several backand forth passes (reversing).

Before rolling, the strip has a strip temperature which is often above adesired set point temperature. The object of the present invention is toprovide a method by which the strip can be brought as quickly aspossible to the desired rolling temperature.

The object is solved in that the strip is removed from the upstreamcoiler with a strip thickness and with a strip temperature above the setpoint temperature, passes with a travel speed through the reverserolling mill with a first reduction per pass of maximally 5%, and iswound up on the downstream coiler, wherein the travel speed is selectedsuch that the strip when being wound up has reached the set pointtemperature.

In this way, the strip is cooled significantly faster than in atemperature compensation furnace.

In practice, the reduction per pass should be selected as minimally aspossible, for example, should be only 1%, because the deformation duringrolling increases the strip temperature again. It is optimal when thefirst reduction per pass is zero, i.e., the rolling mill therefore actsonly as a driver with an empty pass.

The desired rolling temperature can be adjusted even more precisely whenthe strip is heated on the coilers, i.e., the reverse rolling mill isdesigned as a so-called Steckel mill.

The method according to the invention can be used especiallyadvantageously for performing hot rolling as well as cold rolling ofsteel in a single rolling mill. It is particularly advantageous when thestrip temperature is above the so-called GOS line and the set pointtemperature is below this line when the metal to be rolled is steel.

The strip thickness, at which the strip temperature is lowered to theset point temperature, is preferably in the range of 5 and 15 mm.

Further advantages and details result from the further claims as well asthe following description of one embodiment. In this connection, in aschematic representation the only

FIG. 1 shows a Steckel mill.

A Steckel mill is comprised according to the FIGURE of a reverse rollingmill 1 with one or two roll stands 2, 3, having arranged upstream anddownstream thereof a coiler 4, 5, respectively. In the Steckel mill astrip 6 is to be rolled, in particular, in an exemplary fashion from abeginning thickness of 50 mm to a final thickness of 1.2 mm. For thispurpose, the strip 6 is rolled in a reversing fashion in the Steckelmill. Accordingly, it is removed from one of the coilers 4, 5, passesthen through the reverse rolling mill 1, and, subsequently, is wound upagain onto the other coiler 4, 5. Subsequently, the operating directionis reversed. Accordingly, the strip 6 is now removed from the other oneof the coilers 4, 5 in the next process step, passes through the reverserolling mill 1, and is then wound up again on the first one of thecoilers 4, 5. Each one of these travels through the reverse rolling mill1 is conventionally referred to as a pass. In order to maintain thestrip temperature T of the strip 6 as constant as possible, the coilers4, 5 are embodied as coiler furnaces in which the strip 6 is heated.

The strip 6 according to the embodiment is a steel strip. The strip 6 isconventionally hot rolled at the beginning. Accordingly, it has a striptemperature T above the GOS line for steel. The strip temperature T is,for example, 1100° C.

The strip 6 is now hot rolled in a reversing fashion in several passeswithin the reverse rolling mill 1 until its strip thickness d is between5 and 15 mm, for example, 10 mm. The further rolling to a finalthickness of 1.2 mm is to be performed by cold rolling of the strip 6.For this purpose, the strip temperature T of 1100° C. is to be loweredto a set point temperature T* for the cold rolling. The set pointtemperature T* is below the GOS line for steel and is thus, for example,700° C.

The lowering of the strip temperature T is carried out as follows.

It is to be assumed that the strip 6 during the last pass of hot rollinghas been wound onto the coiler 4, in the following referred to as theupstream coiler 4. The strip 6 is now removed at its strip temperature Tfrom this upstream coiler 4 and passes through the reverse rolling mill1 at a travel speed v. After passing through the reverse rolling mill 1,the strip 6 is wound onto the other coiler 5, in the following referredto as the downstream coiler 5.

The reduction per pass in the reverse rolling mill 1 is adjusted forthis pass as low as possible. Ideally, the reduction per pass is zero.The roll stands 2, 3 of the reverse rolling mill 1 in this case act onlyas a driver for the strip 6. However, a minimal reduction per pass of,for example, 1%, in any case however of maximally 5%, can be tolerated.The travel speed v can be selected essentially as desired for such aminimal reduction per pass. In particular, the travel speed v can beselected also to be very small. The strip 6 has therefore sufficienttime to cool over the travel distance between the two coilers 4, 5 tothe set point temperature T*. When being wound up, the strip 6 cantherefore have the set point temperature T* of, for example, 700° C.

The now subsequently performed cold rolling is carried out in principleidentically to the aforementioned hot rolling. The reverse rolling millaccordingly acts again as a normal rolling mill which reduces the stripthickness d of the strip 6 with each pass, in particular, generally by20 to 50%, sometimes even by 60% per pass. Only the last pass to reachthe final thickness of, for example, 1.2 mm, is usually performed with asmaller reduction per pass of approximately 10%.

Should it not be possible, because of technical conditions, to selectthe travel speed v of the strip 6 so small that the lowering of thestrip temperature T to the set point temperature T* can be performed ina single pass, two or more such cooling passes can be performed, ifdesired, before the process is continued with further rolling, in thisconnection, cold rolling.

LIST OF REFERENCE NUMERALS

1 reverse rolling mill 2, 3 roll stands 4, 5 coiler 6 strip d stripthickness T strip temperature T* set point temperature V travel speed

What is claimed is:
 1. A rolling method for a metal strip (6) in areverse rolling mill (1) with an upstream and a downstream coiler (4,5), wherein the strip (6) with a strip thickness (d) is removed from theupstream coiler (4) at a strip temperature (T) above a set pointtemperature (T*), passes through the reverse rolling mill (1) with afirst reduction per pass of maximally 5% at a travel speed (v) and iswound up by the downstream coiler (5), wherein the travel speed (v) isselected such that the strip (6) has reached the set point temperature(T*) when being wound up, and wherein the strip (6) is then removedsubsequently from the downstream coiler (5), passes through the reverserolling mill (1) with a second reduction per pass of at least 10%, andis wound up by the upstream coiler (4).
 2. The rolling method accordingto claim 1, wherein the first reduction per pass is maximally 1%.
 3. Therolling method according to claim 2, wherein the first reduction perpass is zero.
 4. The rolling method according to claim 1 wherein thesecond reduction per pass is at least 20%.
 5. The rolling methodaccording to claim 1 wherein the strip (6) is heated in the coilers (4,5).
 6. The rolling method according to claim 1 wherein the metal stripis comprised of steel, that the strip temperature (T) is above the GOSline for steel, and that the set point temperature (T*) is below the GOSline for steel.
 7. The rolling method according to claim 1 wherein thestrip thickness (d) is between 5 and 15 mm.